Ships are used extensively in the oil industry for carrying out work related to drilling oil wells and/or recovering oil from wells that have been drilled offshore. Well known marine waters include those such as in the North Sea and the Gulf of Mexico. Ships arranged for drilling oil wells and support ships for carrying out related work have to be able to maintain a position or course and position in order to carry out or assist in carrying out operations related to exploratory work, drilling, offloading samples, offloading oil, transferring supplies and so on.
Dynamic Positioning (DP) is a process for regulating the propellers or thrusters of a ship in order to maintain the ship at a position or on a course heading. The DP processes and procedures are typically computer controlled and may include a computer model representing the ship and also may model the actions of external forces such as wind, waves, tides etc. on the ship. The propellers, thrusters or other propulsion devices of the ship are continually or dynamically regulated in respect of thrust and thrust direction so as to counter effects of wind, waves, tides, currents and maintain a position. In this way a relative position, relative to another ship or to an object on the seabed, or an absolute position relative to eg a GPS position can be maintained dynamically even when the wind or tides or currents etc. vary from time to time.
In various DP class notations there are specific requirements to have a spinning reserve connected to the power plant. The term spinning reserve may be understood to refer to a generator and engine or other prime mover, a generator set, which is running at a low speed or idling. The prime mover can be accelerated up to a higher operating speed more quickly than a generator set could be started from a standstill and then brought up to speed. Thus in DP operations the spinning reserve is provided as a form of reserve power capacity in the “unused” spinning reserve connected to the power plant, capable of quickly delivering power in the event of a failure in rotating machinery or a sudden load increase. However, the spinning reserve requirement forces the combustion engine to run at a lower average power output, leading to a power plant running at a sub-optimum point with respect to fuel consumption. There is also a time lag between making a demand for a higher electrical power output from an idling generator set and delivery of a higher level of electrical power. The inventors have determined a need for an improvement to spinning reserve technology.